Cardiac resynchronization therapy (CRT) is a treatment for heart failure patients in which one or more heart chambers are electrically stimulated (paced) to restore or improve heart chamber synchrony. CRT therapy involves biventricular pacing which consists of pacing the right ventricle (RV) with a RV electrode and a left ventricle (LV) with a LV electrode or monoventricular pacing which consists of pacing only the left ventricle. Achieving a positive clinical benefit from CRT depends in part on the location of the pacing site, particularly in the left ventricle (LV). Placement of the pacing leads and selecting electrode pacing sites is important in promoting a positive outcome from CRT. Multi-site pacing in a given heart chamber may potentially achieve greater restoration of heart chamber synchrony and therapeutic benefit. Efforts have been made to perform multisite pacing, as has been shown and described in U.S. Pat. No. 8,509,890 B2 to Keel et al., U.S. Pat. No. 5,267,560 to Cohen, U.S. Pat. No. 5,174,289 to Cohen, U.S. Pat. No. 6,496,730 to Kleckner et al. The INSYNC II MARQUIS™, a CRT device manufactured by Medtronic, Inc., and the INSYNC III MARQUIS™ were configured to perform at least one of sequential and/or simultaneous pacing to two different ventricular tissue sites.
Multi-site pacing requires a charge to be delivered through a pacing path and a recharging path that removes excess charge at a tissue-electrode interface due to pacing. The pacing path includes an output capacitor that generates a pacing pulse to the impedance load formed by electrodes, a coupling capacitor, and the patient's heart tissue between the electrodes. The recharging path has a current that follows an opposing direction of the pacing path. The recharging path includes the tissue-electrode interface and a coupling capacitor that can absorb residual post-pace polarization signal (or “after-potential”). Residual post-pace polarization signal is undesired since sensing of a response from tissue to a pacing pulse can be affected. Exemplary tissue-electrode interfaces that can absorb residual post-pace polarization signal and subsequently discharge the polarization signal are located at the active tip electrode and the indifferent ring (or IPG case or “can”) electrode.
Sense amplifiers are typically “blanked” during the delivery of the pacing pulse and a programmed blanking period until the repolarization of the tissue-electrode interfaces operation occurs. “Blanked” sense amplifiers means the sense amplifiers are uncoupled from the pace/sense electrodes. “Blanked sense amplifiers, for example, prevent saturating the front end amplifier of the sensing circuit. Most current pacemaker output amplifiers circuits incorporate “fast recharge” circuitry for short circuiting the pacing path and actively dissipating or countering after-potentials during the blanking of the sense amplifier's input terminals to shorten the time that it would otherwise take to dissipate post-pace polarization signal. Fast recharge circuitry and operations are described in commonly assigned U.S. Pat. Nos. 6,324,425, 4,406,286, and 5,782,880, and German OLS DE 196 15 159, all incorporated herein by reference. One purpose of a recharge operation is to address net charges that occur due to redox reactions which generate gases (e.g. H2, O2, Cl2) at the electrode interface. Recharge operations ensure that the coupling capacitor(s) is recharged to an insignificant voltage level or equilibrium prior to the delivery of the next pacing pulse. By ensuring the net DC current in the pacing path settles to zero or nearly zero, corrosion of the electrode is prevented. In contrast, electrode corrosion does occur when an ineffective recharging path causes a net charge to remain after a pacing pulse is delivered. U.S. Pat. No. 6,324,425 employs predetermined recharge time periods to ensure that the coupling capacitor(s) is recharged to an insignificant voltage level or equilibrium.
It is desirable to develop systems and/or methods that are not limited to predetermined recharge time periods. It is also desirable to develop additional systems and/or methods that are able to increase pacing and/or recharge configurations to optimize resynchronization therapy and reduce side effects such as phrenic nerve stimulation.